Electron discharge device and method of fabricating the same



K. H. KINGDON ELECTRON DISCHARGE DEVICE AND METHOD OF FABRICATING THESAME July 14;, 1931,

Filed March 6, 1926 Inventor Kenneth HKinQdon,

b Hus Attorney.

. Patented July 14, 1931 UNITED STATES.

PATENT OFFICE KENNETH H. KINGDON, OF SCHENECTADY, NEW YORK, ASSIGNOR TOGENERAL ELEC- TRIC COMPANY, A CORPORATION OF NEW YORK ELECTRON DISCHARGEDEVICE AND METHOD OF FABRICATING THE SAME Application filed March 6,1926. Serial No. 92,946.

. The present invention comprises improvetion which are set forth withgreater parments in electronlc devices containing a conducting materialof relatively high vapor pressure, such as an alkali metal, and its mainobject is to prevent impairment ofthe efliciency of such devices by theformation of a conducting film on the inner surface of the container,which would permit electrical leakage to occur between sealed-inconductors. As the conducting film is mainly deleterious when formed onthe glass stem of these devices, through which the leadingin wires aresealed, the phenomenon will be referred to herein as stem leakage.

' In a bulb containing electrodes operating at a higher temperature thanthe bulb, an easily vaporizable material is continually vaporizing atthe electrodes and condensing on the cooler bulb. Under some conditionsthe condensed material forms a continuous film which, even when it is sothin as to be invisible to the unaided eye, has a sufiiciently highelectrical conductivity to cause serious electric leakage.

I have found that under other controllable conditions the vapor willcondense in detached specks between'which there is no electricalcontact, and which will not cause electrical leakage.

It is my present opinion that the continuous deposit occurs when tthevapor is adsorbed by a layer of oxide or a thin metallic film on thesurface of the stem, or other part of a tube, over which leakage occurs.The formation of this adsorbing film apparently is promoted by thedeposition of the products of ionization of gas on the stem.

In accordance with the present invention discontinuity in the condensedmetal on the surface of the stem, or wherever electrical.

leakage is like to occur, is obtained by carrying out the exhaust inaccordance with a procedure hereinafter described and also by aconstruction whereby ionization in the space adjacent the stem isavoided. The exhaust procedure appears to owe its effectiveness to theactionof water left in the glass which converts the deleterious oxide tohydroxide.

The novel structural features of my inventicularity in the appendedclaims are illustrated by the accompanying drawing in which Fig. 1 showsin perspective one form of a complete device; Fig. 2 shows theelectrodes in perspective on a somewhat larger scale, the anode beingshown in part broken away, and Fig. 3 is a fragmental perspective viewof a modification, the enclosing bulb being omitted in Figs. 2 and 3.

Referring to the drawings, the device shown in Figs. 1 and 2 comprises asealed envelope 1, commonly consisting of glass on the stem 2 of whichare mounted the electrodes of the device. The electrode leading-inconductors are sealed into the stem and connected to the exteriorcontacts of a base 3. As shown in Fig. 2, the cathode of the deviceconsists of a filament 4 which has in the main a rectilinear extensionbut which actually consists of a fine spiral wire. This cathode, whichmay consist of tungsten is connected to a support 5 which serves also asa current supply conductor and therefore is sealed into the stem 2. Theopposite end of the cathode filament is connected to the sealed-inleading-in conductor 7. As indi cated in the drawings, the ends of thecathode may be connected to short pieces of somewhat heavier nickel wirewhich in turn are connected to the still heavier wires 5, 7 The anode 8is cylindrical in form and inclosesthe cathode substantially throughoutits length. The anode is provided upon its interior with four vanes 10which extend radially toward the cathode. The anode is supported bystout anchor wires 11, 12, one of which passes through the stem 2 andserves as a leading-in conductor. Between the vanes 10 there is provideda second set of vanes which are constituted of metal plates 9, 13 bentin such a way as to extend radially from the cathode filament toward theanode. The vanes 9, 18, are supported by a plate 14.- which isconveniently made circular in form and is positioned closely adjacentbut out of contact with the lower end of the cylindrical anode 8. Thevanes 9, 13 therefore are electrically at the same potentialv andtogether constitute the control electrode of grid of the device. Boththe anode and the control electrode may consist of nickel. The plate 14,together with the grid members 9, 13, are supported upon wires 15, 16,one of which is sealed into the stem 2 and serves to impress potentialchanges upon the grid. The plate 14, WhlCh is rovided with a holethrough which the cat ode wire passes, serves to prevent the'escape ofelectrons from the space between the electrodes and thus Ereventsionization from occurring around t e stem.

e device is also provided with a capsule 17 consistin of two metalIplates, a cavity being rovided in one of t e lates in which is p aced asmall quantity 0 a reaction mixture capable of yielding an alkali metal,such as caesium. For example, a mixture of caesium chloride and metalliccalcium the formation of a continuous,

or magnesium may be used. The capsule 17 is supported any convement wayas by a wire 18 connected to the anode. As shown in Figs. 1 and 2, thecapsule 17 is in a position somewhat above the anode so that it may beheated by a high frequency field independently of the anode.

The bulb should not be subjected during exhaust to the high temperaturebake-out to which vacuum devices usually are subjected. It may be bakedfor about half an hour at a temperaturesomewhat below 300 C. During orafter this partlal dehydratlon of the bulb, gas may be driven from theelectrodes, by heating the same by high freuency induction or otherconvenient way. 2 liquid air trap in the vacuum system s a somewhat tooenergetic agent for removing water vapor. Pre erably aside bulbcontaining phosphorous pentoxide is used instead of a liquid air trap,care being taken to avoid introduction of the pentoxide into the bulb.It is my present opinion that moisture left in the glass by thisprocedure converts traces of oxide or alkali metal deposited on the stemto hydroxide and thus produces a surface condltion unfavorable toelectrically conducting film.

The tungsten cathode preferably should be provided with an oxygenoussurface by heating in an atmosphere of attenuated oxygen or air so as torender its surface suitable for the adsorption of a thin film of caesiumduring operation. For example, after exhaust oxygen at a pressure ofabout 100 microns of mercury may be admitted to the bulb, the filamentis then heated to about 2000 K. for about one minute to produce a thinadherent film of oxygen. The oxy then is exhausted and the capsule 17 isheated to liberate caesium. The thin film of caesium adsorbed by thecathode permits of efiicient emission of electrons when the cathode isoperatedv at a temperature of about 950 K. which would otherwise be toolow to produce gen' appreciable electron emission from ordinary tungstenin a vacuum. The phenomena involved in the emission of electrons from atungsten cathode in the presence of caesium vapor are described in apersin The Proceedings of the Royal iety, A Vol. 107, p. 61, 1925, andPhysical Review, Vol. 24,p. 510, 1924, and therefore will not bedescribed in detail in the present specification. It is desirable alsoto have present in the bulb a source of oxygen, such as a small piece ofoxidized copper indicated at 19. During the operation of the tube someof the caesium reacts with the cop r oxide to form caesium oxide and theresulting mixture of caesium and caesium oxide eliminates deleteriousgases such as hydrogen and carbon monoxide when evolved in minutequantities from metal and glass parts of the device.

The shield 14 may assume various forms and modifications within thescope of my invention. In Fig. 3, I have illustrated a modified shield20 which surrounds the stem 2 leaving the electrodes 21 (shown in part)otherwise unshielded. This shield '20 is supported by the nickel wirewhich in turn forms an anchor for the lower end of the cathode. The twomembers constituting the anode are connected together by a wire (notshown) across the top and similarly the two grid members, which areinserted between the slots of the anode elements, are also connectedtogether at the top by a wire (not shown). The stem shield 20 largelyprevents contact of products of ionization with the stem, and thuspreserves discontinuity in the deposits of alkali metal condensedthereon device.

Devices containing caesium constructed and exhausted as above describedhave been operated successfully as amplifiers for 1000 hours or morewith 60 volts on the anode, and the grid being connected to the negativeend of the cathode filament.

at I claim as new and desire to secure by Letters Patent of the UnitedStates, is,-

An electrical discharge device comprising an evacuated container,electrodes having supply conductors sealed closely adjacent one anotherinto said container, and a charge of alkali metal in said container, theinner surface of said container adjacent the seals for said electrodescontaining suflicient water to cause alkali metal condensed on saidsurface to assume the form of discontinuous specks incapable of causingsubstantial electrical leakage between said electrodes.

In Witness whereof, I have hereunto set my hand this 5th day of March,1926.

KENNETH H. KIN GDON during the operation of the

